Applications of biological and chemical sensors stimulate the demand and development of ultra-sensitive devices to detect bio-molecules with very low concentrations.
Micro-resonators sensor and photonic crystal sensor (PCs) have been proposed for sensing analytes at low level. These devices offer an advantage of reducing the device size by orders of magnitude without sacrificing the interaction length by virtue of their high quality-factor (Q) resonance. The resonance effect provides an equivalently long interaction length to achieve a sufficient phase shift. Such a property can dramatically reduce the device size and the amount of analytes needed for detection.
However, micro-resonator sensors still rely on evanescent wave sensing scheme which make it difficult to further reduce device size and the amount of analytes needed for detection. A high sensitive disk resonator has been demonstrated by A. M. Armani et al. (“Label-free, Single-molecule Detection with Optical Microcavities”, Science, Vol. 317, pp.783-787) for single molecule detection by improving Q value. However, to achieve the ultra-high Q value, the disk edge has to be melt by laser to form a smooth and stress-free surface. Such a process is difficult to control and not suitable for mass production.
Photonic crystals, unlike many sensing platforms that utilize the interaction between the small evanescent tail of the electromagnetic field and the analyte, confine a high electric field in the small modal volumes and provide efficient light-matter interaction with minuscule volumes of analyte. However, to improve the confinement, the index contrast has to be increased. Then the geometrical features not only become very small but have to be very accurately fabricated. This results in significant challenge in fabrication of PC sensors.
It is an object of the present invention to provide a high sensitive optical resonator which is easy to be fabricated at low cost.